The present invention generally relates to an RF coupler. More specifically, the present invention relates to a multi-band coupled-line coupler.
Couplers are well known in the art. They are used in radio frequency (RF) applications. For example, a coupler can be used in a communication device such as a cellular telephone set.
U.S. Pat. No. 4,216,446 discloses an improvement in directivity and isolation of a quarter wave microstrip directional coupler. The improvement is achieved with the addition of a single capacitor placed across the directive port of the coupler. This patent also discloses a dual coupler scheme but with emphasis on using both coupling lines for single frequency applications.
U.S. Pat. No. 4,376,921 discloses a loosely coupled microstrip coupler with high directivity. A capacitive coupling element is disposed within the coupling region across the main and coupled transmission line sections for supplementing the dielectric capacitive coupling of the gap therebetween to increase the directivity of signal coupling. The reduction of coupler length is realized through adding a series inductor and a parallel resistor to the second coupled line output.
U.S. Pat. No. 5,424,694 discloses a miniature directional coupler. The coupled lines have a length considerably less than one quarter of a wavelength.
U.S. Pat. No. 5,576,669 discloses a coupling device for coupling RF energy. The device includes a first coupling structure and second coupling structure. The addition of the first coupling structure and the second coupling structure allows for a greater coupling efficiency.
The contents of the aforementioned U.S. Pat. Nos. 4,216,446, 4,376,921, 5,424,694, and 5,576,669 are incorporated by reference to the extent necessary to understand the present invention.
The present invention is directed to a multi-band coupled-line coupler for RF power amplifier module applications. The coupler comprises a first conductor having a first and a second end portion and a first parallel portion therebetween; a second conductor having a first and a second end portion and a second parallel portion therebetween, the second parallel portion positioned substantially parallel to the first parallel portion; a common conductor having a first and a second end portion and a third parallel portion therebetween, the third parallel portion positioned substantially parallel to and between the first and second parallel portion, the third parallel portion having a first distance from the first parallel portion and a second distance from the second parallel portion, the first distance being different from said second distance; a first capacitor connected between a point on the first parallel portion and a point on the third parallel portion; and a second capacitor connected between a point on the second parallel portion and a point on the third parallel portion.
The present invention is also directed to a communication device having a multi-band coupled-line coupler. The coupler comprises a first conductor having a first and a second end portion and a first parallel portion therebetween; a second conductor having a first and a second end portion and a second parallel portion therebetween, the second parallel portion positioned substantially parallel to the first parallel portion; a common conductor having a first and a second end portion and a third parallel portion therebetween, the third parallel portion positioned substantially parallel to and between the first and second parallel portion, the third parallel portion having a first distance from the first parallel portion and a second distance from the second parallel portion, the first distance being different from said second distance; a first capacitor connected between a point on the first parallel portion and a point on the third parallel portion; and a second capacitor connected between a point on the second parallel portion and a point on the third parallel portion.
The communication device may also have a power detector connected to the first end portion of the common conductor; an termination connected to the second end portion of the common conductor; a GSM amplifier connected to the first end portion of the first conductor; a DCS/PCS amplifier connected to the first end portion of the second conductor; a GSM harmonic filter connected to the second end portion of the first conductor; and a DCS/PCS harmonic filter connected to the second end portion of the second conductor. The communication device may also have a switch having at least a first and a second position, the first position connecting the circuits of the first and common conductor, the second position connecting the circuits of the second and common conductor.